Well, having a 120v/LPG 2 way Norcold, I’ve admittedly not thought much about running a refer on DC, mainly because of the limited battery capacity on the typical TC…I have space for two 6v GC’s wet-cells, so I figure a gross practical capacity at about 200 amp/hrs in total, with about 100 amp/hrs usable…(not including the possibility of solar harvesting or generator).
Assuming the dc compressor Norcold has about 20min of duty cycle (might be slightly less < >), it’s published 3.2a consumption would suggest the use about 25 amps of this aforementioned 100 amp/hrs available per day…This would still leave a theoretical 75 usable amp/hrs remaining before getting to the 50% DOD point (depth of discharge)…
The compressor Norcold seems to me to be uber electrically efficient, and the LPG savings seems somewhat intriguing (especially when going off the grid), but for us, with only two Batteries (assuming little solar harvest) would not leave much reserve battery capacity – once evening sets in, we might use yet another 25 amp/hrs till morning comes – this assumes batteries starting out at about 95-100% SOC (state of charge) along with typical evening activities, colder wx (requiring furnace ops), and morning coffee via ProSine 2.0 inverter…
Though quite pricey ($$), one might consider using Lithium batteries due to their smaller size (about half the size and weight) and because they are relatively ‘voltage stable’ and happy even when discharged down to a much deeper DOD (say 80% or so) without damage (meaning, more ‘usable’ amp/hr capacity from the same gross amp/hrs), and should also consider lots of solar – the solar route is likely a much cheaper option, but harvest will vary depending on conditions…
Lithium will also require a lithium specific on-board charger and solar charge controller…
I have 440w of solar which usually (WX dependent) does a great job of keeping the batteries charged, but the harvest would be even further optimized (shortening harvest times) were I to upgrade to AGM’s which are faster at recovering than are wet-cells…Also bare in mind that compressor motors tend to have to work harder as the nominal 12v battery voltage declines (advantage, lithium), thus the more conventional batteries the better…
As it is, the only time I run the portable Honda 2200 is when running the air conditioner…FWIW, I switched out the power sucking 30kbtu Suburban furnace with a far more efficient (by over 50%) Atwood two speed 15/22kbtu – this alone made a huge difference, along with LED lamps…
Ultimately, it’s all about trade-offs, lol…
